Plyometric Training in Prepubertal Soccer Players: Is It Really Effective for Soccer Performance?

Abstract

Background/Objectives: Plyometric training is a method of increasing soccer performance which leverages the muscle stretch-shortening cycle. This study aimed to evaluate the safety and effectiveness of plyometric training in prepubertal soccer players. Methods: Twenty-three young athletes (age 9.4 ± 0.3 years) from an elite club, training three times per week, were enrolled. During one of the weekly training sessions, twelve players formed the experimental group (PLYO), incorporating a 45 min plyometric training component into their routine, while the control group (CON), consisting of eleven players continued with their usual training program. At baseline and after 12 weeks, anthropometric parameters, flexibility, lower limb strength, and agility were assessed. Results: At baseline, no differences were observed between the two groups in anthropometric or physical performance parameters. No injuries occurred during the study. After 12 weeks, both groups showed significant growth and performance improvements. However, the PLYO showed a significantly greater increase in lower limb strength (Δ + 10.7%) compared to the CON (Δ + 6.0%). Conversely, although not statistically significant, agility improvements were greater in the CON (Δ + 12.4%) than in the PLYO (Δ + 8.6%). Conclusions: Plyometric training appears to be a safe and effective method for enhancing lower limb strength in prepubertal athletes. However, this strength gain did not directly translate into greater agility, which may benefit more from sport-specific training during this developmental stage.

1. Introduction

During official matches, young soccer players cover approximately 230 m through high-intensity activities, performing up to 50 sprints. These activities require young athletes to engage in frequent acceleration and deceleration patterns [1]. Recently, the concept of the most demanding passages of play has gained attention [2]. This term refers to periods in a match during which players perform at peak intensity, often coinciding with key technical or tactical moments. As such, a strong link has been established between high-intensity physical performance and crucial phases of gameplay.

Simultaneously, research has focused on training methods aimed at improving physical abilities and skills directly linked to high-intensity soccer performance. Acceleration and deceleration patterns are prevalent during direction-change tasks, as well as during various locomotor activities such as lateral and backward running [3]. As a result, training programs should incorporate rapid transitions between eccentric and concentric muscle contractions, engaging fast-twitch fibers during motor activities performed at intensities above 90% of maximum intensity [4].

The plyometric training (PT) method is associated with neural adaptations and increased rates of power development and movement velocity [5]. This approach involves rapid transitions between eccentric and concentric muscle activities, commonly referred to as the stretch-shortening cycle. PT typically includes bodyweight jumping exercises that enhance the neural and musculotendinous systems’ ability to generate maximal force in minimal time. Despite its high intensity demands, Rumpf et al. [6] have demonstrated that PT is an effective and safe method to improve performance in youth athletes. While PT may initially appear traumatic due to its ballistic movements, children develop enhanced inhibitory mechanisms to protect the muscle-tendon unit. These mechanisms include increased co-contraction, heightened antagonist activation, reduced pre-activation, and diminished stretch reflexes [7,8].

Training programs incorporating horizontal and vertical plyometric exercises significantly improve muscle power, sprinting, jumping, and direction-change performances in young soccer players [9,10]. However, debates persist regarding the optimal planning of PT programs, particularly concerning: 1. the duration [11] of the intervention (number of the session required) and 2. the number of ground contacts per training session [12]. Studies indicate that PT effectively improves jumping and sprinting performance after interventions lasting at least seven weeks with a minimum of two sessions per week. Longer interventions often yield greater results, particularly for young soccer players undergoing gradual performance development. Regarding ground contacts—defined as the number of stretch-shortening cycles during PT—a total of 60 [13] or 100 [12] foot contacts per session has been deemed sufficient to enhance jump height and direction-change performance. PT shows particular efficacy in adolescents (up to 17 years of age), as the maturation process amplifies performance improvements following peak height velocity (PHV).

The study aims to evaluate the effectiveness of PT in improving jump, sprint, and direction-change performances in young elite soccer players before reaching PHV. This study hypothesizes that a PT program incorporating: 1. a gradual increase in the number of ground contacts; 2. a sufficient duration to achieve the expected physical adaptations; and 3. a single PT session within the weekly training program, is effective and safe even in the prepubertal phase of young elite soccer players.

2. Materials and Methods

2.1. Participants

The study was conducted at a single elite soccer club (Empoli Football Club), with all participants recruited from the same Under-10 team.

Inclusion criteria were as follows: membership in the Under 10 elite team, at least 4 years of soccer experience, active participation in competitive sports, possession of valid sports eligibility certification, affiliation with the same club and team, and the absence of conditions preventing regular participation in weekly training sessions.

Exclusion criteria included the presence of injuries or clinical conditions at the time of enrollment.

A total of 26 young soccer players were initially assessed for eligibility. Of these, 3 were excluded at the start of the study due to previous musculoskeletal injuries.

All athletes voluntarily participated after receiving a detailed explanation of the procedures and methodology, and they provided written informed consent in accordance with the Declaration of Helsinki (2013). Ethical clearance was obtained from the Tuscany Region as part of the Regional Prevention Plan (n. O-Range18). Data were processed anonymously.

2.2. Study Design

This randomized controlled trial was conducted during the in-season period. Twenty-three participants (age: 9.4 ± 0.3 years) were randomly assigned to either an experimental group (n = 12) and a control group (n = 11).

The experimental group (PLYO) participated in a plyometric strength training program conducted once a week for 45 min during one of their three weekly team training sessions, over a 12-week period. Following the warm-up, players were divided into two groups (PLYO and CON) for 45 min before reconvening at the end of the session. The decision to include only one plyometric training session per week was made to maintain the ecological validity of the training program, as increasing the frequency of plyometric training has not been shown to provide additional benefits for prepubertal male soccer players [14].

The control group (CON) followed the standard training program during the same 45 min period, focusing on motor skills, technical abilities, and tactical aspects, without the inclusion of plyometric exercises. Evaluations to assess the effectiveness of the plyometric training program were conducted at baseline (T0) and after three months (T1). The CONSORT [15] flowchart of the study design is shown in Figure 1.

2.3. Plyometric Training Program

The PT program consisted of three mesocycles of four weeks each, with progressive training loads.

• Mesocycle 1 included squats, hip hinges, hurdle sprints, snap-downs, and drop squats.
• Mesocycle 2 introduced countermovement jumps, hurdle jumps, and hurdle squats.
• Mesocycle 3 added bounding jumps, hop jumps, pogo jumps, and pogo hopping.

The number of ground contacts increased progressively: 90–100 in the first mesocycle, 130–140 in the second, and 170–180 in the third (

Table 1. Twelve weeks of plyometric training program. The numbers in the table indicate the sets and reps (sets x reps) for each exercise during the 3-month training program. Rest between sets was 2 min.

Plyometric Training Program
	Month 1				Month 2				Month 3
	Week 1	Week 2	Week 3	Week 4	Week 5	Week 6	Week 7	Week 8	Week 9	Week 10	Week 11	Week 12
Squat	4 × 6	4 × 6	4 × 6	4 × 3	4 × 3
Hip Hinge	4 × 6	4 × 6	4 × 6	4 × 3	4 × 3
T.U.T. Squat	4 × 6	4 × 6
Hurdle Sprint		4 × 6		4 × 3			4 × 6		4 × 10			4 × 10
Snap Down			4 × 6	4 × 6	4 × 6	4 × 6	4 × 6
Hurdle Squat			4 × 6	4 × 6
Drop Squat				4 × 6	4 × 6	4 × 6	4 × 6
Box Jump					4 × 10	4 × 6
Hurdle Jump						4 × 10	4 × 6	4 × 10		4 × 10	4 × 10
Countermovement Jump							4 × 10	4 × 10
Pogo Jump								5 × 12	4 × 10	4 × 6	4 × 6	4 × 6
Bound Jump									4 × 6	4 × 6	4 × 6	4 × 6
Hop Jump									4 × 6	4 × 6	4 × 6	4 × 6
Pogo Hopping									4 × 6	4 × 6	4 × 6	4 × 6
Depth Squat										4 × 10	4 × 10
Sprint												4 × 10

). This gradual increase in training volume was designed to minimize the risk of injury due to overload.

2.4. Physical Performance Test

Assessments included anthropometry, lower limb flexibility, strength, and agility. One week prior to the start of the study, athletes participated in a familiarization session to ensure familiarity with all testing procedures.

On the testing day, anthropometric and flexibility tests were performed indoors before training under controlled environmental conditions. Strength and agility tests were conducted on the soccer field following a standardized 15 min warm-up. All assessments were performed during afternoon training sessions, at the same time of day, to control for diurnal variations.

The test battery included:

-

Height and sitting height were measured to the nearest 0.1 cm using a stadiometer (SECA^® 240, Hamburg, Germany), and weight was recorded to the nearest 0.1 kg using calibrated scales (SECA^® 877, Hamburg, Germany). Biological age was calculated using the Mirwald [16] formula based on anthropometric and chronological data.

-

Sit-and-reach test: Athletes sat on the floor with extended legs, reaching forward without knees flexion. The distance from the fingertips to the toes was measured in centimeters. Positive values indicating greater torso flexion and posterior leg muscle flexibility [17].

-

Standing Long Jump Test: Athletes jumped as far as possible from a standing static position, aiming to land with both feet together. They started with feet shoulder width apart, with no restriction on arm movement. The jump distance was measured from the last heel strike to the take-of line.

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Triple Jump: Athletes began at the starting line and performed three consecutive maximal forward jumps, alternating the supporting leg. No run-up was allowed, but arm swing was permitted. Total distance was measured from the start point to the final landing.

-

The t agility test: Athletes ran a forward, lateral, and backward course, maintaining a forward-facing posture without crossing their feet. Completion time was recorded in seconds measured using dual-beam photocells (Witty Gate, Microgate Srl, Bolzano, Italy) [18].

Each test was performed three times, and the average value was used for analysis.

2.5. Statistical Analysis

The normality of data distributions was assessed using the Shapiro–Wilk test. Descriptive statistics were reported as mean ± standard deviation (SD). A two-way repeated-measures ANOVA (Time × Group) was conducted for each anthropometric and physical performance variable to evaluate the effect of the intervention, while homogeneity of variances was verified with Levene’s test. When significant interaction effects were observed, Bonferroni-adjusted pairwise comparisons were used. Effect sizes for the main and interaction effects were reported using partial eta squared (η²_p). For pairwise post hoc comparisons, Cohen’s d was calculated and interpreted according to conventional thresholds: small (<0.20), medium (<0.60), and large (≥0.80). The level of statistical significance was set at p ≤ 0.05 for all analyses [19]. Statistical analyses were performed using JASP version 0.18.2 (JASP Team, Amsterdam, The Netherlands).

3. Results

During the three-month training period, no muscle injuries or overuse-related conditions attributable to the plyometric intervention were reported.

3.1. Anthropometric Parameters

The repeated-measures ANOVA revealed a significant main effect of time for all anthropometric variables, including height, body mass, sitting height, chronological age, and biological age. These results indicate that both groups experienced significant growth over the 12-week period, likely due to natural maturation processes. However, no significant main effects of group or interaction effects were found (

Table 2. Differences at baseline and at three-month intervention values in anthropometric parameters between the plyometric training group (PLYO) and in the control group (CON).

Variable	Group	T0	T1	Time Effect (p)	Group Effect (p)	Interaction (p)
Height (cm)	PLYO	152.8 ± 6.4	156.8 ± 6.2	<0.001	n.s.	n.s.
	CON	155.9 ± 7.3	160.5 ± 6.8
Mass (kg)	PLYO	43.6 ± 7.3	44.9 ± 7.9	<0.001	n.s.	n.s.
	CON	46.1 ± 6.8	48.1 ± 7.2
Sitting height (cm)	PLYO	79.3 ± 3.5	81.6 ± 4.3	<0.001	n.s.	n.s.
	CON	79.9 ± 3.6	81.9 ± 3.4
Chronological age (yrs)	PLYO	9.4 ± 0.3	10.2 ± 0.2	<0.001	n.s.	n.s.
	CON	9.3 ± 0.2	10.0 ± 0.4
Biological age (yrs)	PLYO	9.2 ± 0.5	10.0 ± 0.6	<0.001	n.s.	n.s.
	CON	9.3 ± 0.7	10.0 ± 0.7

).

3.2. Physical Performance Parameters

At baseline (T0), no significant differences were observed between the PLYO and CON in any physical performance test. Following the 12-week intervention, both groups showed improvements in flexibility, lower limb strength, and agility. The results of the two-way repeated-measures ANOVA are summarized below and detailed in Table 3.

-

Flexibility (Sit-and-Reach Test): a significant main effect of time was found (p < 0.001, η²_p = 0.61), indicating overall improvement across both groups. The interaction effect was not significant (p = 0.87), and post hoc comparisons revealed no difference in the magnitude of change between groups.

-

Lower Limb Strength (Standing Long Jump and Triple Jump): for both tests, significant main effects of time were observed (p < 0.001), with large effect sizes (η²_p = 0.95 for Standing Long Jump; η²_p = 0.92 for Triple Jump), indicating meaningful improvements. Significant interaction effects were detected for both tests (p < 0.001), with post hoc analyses showing a significantly greater increase in the PLYO.

-

Agility (T-agility Test): the main effect of time was significant (p < 0.001, η²_p = 0.45), confirming overall improvement. However, the interaction effect was not significant (p = 0.49), and post hoc comparisons showed no statistically significant difference between groups, although the control group exhibited slightly higher Δ% values.

Table 3. Differences between baseline and three-month intervention values in physical performances parameters in the plyometric training group (PLYO) and in the control group (CON).

Test	Group	T0	T1	Δ%	Time Effect (p, η2p)	Interaction (p, η2p)	Post Hoc
Sit-and-Reach (cm)	PLYO	42.5 ± 5.6	43.7 ± 4.9	+2.9	<0.001, 0.61	0.87, 0.001	n.s.
	CON	40.7 ± 7.1	41.9 ± 6.5	+2.8
Standing Long Jump (cm)	PLYO	185.4 ± 17.0	207.6 ± 19.0	+10.7	<0.001, 0.95	<0.001, 0.65	<0.001
	CON	189.5 ± 17.9	201.6 ± 18.8	+6.0
Triple Jump (cm)	PLYO	218.2 ± 47.2	244.3 ± 54.0	+10.8	<0.001, 0.92	<0.001, 0.48	<0.001
	CON	241.8 ± 52.8	256.3 ± 55.9	+5.6
T-agility test (s)	PLYO	11.8 ± 0.5	10.9 ± 0.6	–8.6	<0.001, 0.45	0.49, 0.02	n.s.
	CON	11.8 ± 0.8	10.5 ± 2.4	–12.4

Table 3. Differences between baseline and three-month intervention values in physical performances parameters in the plyometric training group (PLYO) and in the control group (CON).

Test	Group	T0	T1	Δ%	Time Effect (p, η2p)	Interaction (p, η2p)	Post Hoc
Sit-and-Reach (cm)	PLYO	42.5 ± 5.6	43.7 ± 4.9	+2.9	<0.001, 0.61	0.87, 0.001	n.s.
	CON	40.7 ± 7.1	41.9 ± 6.5	+2.8
Standing Long Jump (cm)	PLYO	185.4 ± 17.0	207.6 ± 19.0	+10.7	<0.001, 0.95	<0.001, 0.65	<0.001
	CON	189.5 ± 17.9	201.6 ± 18.8	+6.0
Triple Jump (cm)	PLYO	218.2 ± 47.2	244.3 ± 54.0	+10.8	<0.001, 0.92	<0.001, 0.48	<0.001
	CON	241.8 ± 52.8	256.3 ± 55.9	+5.6
T-agility test (s)	PLYO	11.8 ± 0.5	10.9 ± 0.6	–8.6	<0.001, 0.45	0.49, 0.02	n.s.
	CON	11.8 ± 0.8	10.5 ± 2.4	–12.4

4. Discussion

This study aimed to evaluate the effectiveness of a plyometric training (PT) program in enhancing physical performance among young elite soccer players before reaching PHV. The absence of new muscle injuries during the intervention confirms the safety of the plyometric method [20] even in prepubertal athletes. To ensure both safety and effectiveness, PT programs for this age group should follow a progressive structure that carefully manages: (1) training load, (2) number of ground contacts, and (3) exercise selection. Such structured progression is critical for minimizing the risk of overuse injuries during growth phases.

Previous research has suggested limited improvements in muscle stiffness and reactive strength index from PT in children aged 9 years compared to older adolescents. However, the present study reported improvements in physical performance parameters in both groups, which can only be partly attributed to natural growth and development. Indeed, the PLYO showed greater improvements in muscle strength than the CON, likely due to the extended duration of the 12-week program, compared to shorter interventions such as the 4-week program by Lloyd et al. [21]. Furthermore, our training program adheres to the six key principles outlined by Sánchez Pastor et al. [22] to achieve maximum reliability, consistency, and effectiveness in strength training interventions.

The selection of horizontal jump tests to assess lower limb strength aligns with soccer-specific performance demands [23], where horizontal force vectors are more crucial for tasks like changes in direction performances than the vertical force vector [24]. Despite greater increases in horizontal strength in the PLYO, assessed through standing long jump and triple jump, these gains did not translate into superior agility performance, assessed with the t-test, compared to the CON. This unexpected finding may stem from the CON’s training program, which included more sport-specific tasks, particularly those involving directional changes. During the 45 min in which the PLYO engaged in PT, the CON performed more soccer-relevant movement drills on the field. During prepubertal development, training programs that prioritize motor skills and coordination may lead to greater agility improvements compared to those focusing primarily on physical conditioning, such as strength. This aligns with the “periods of accelerated gains” framework proposed by Lloyd and Oliver [25], which highlights the importance of multilateral stimuli and diverse motor experiences during early developmental stages. Similarly, Van Hooren et al. [26] emphasize that long-term training programs should account for sport-specific skills, muscle group demands, and movement patterns. While analytical PT effectively improves strength, its limited specificity to soccer-related tasks may reduce its direct transfer to agility performance. Consequently, it can be hypothesized that to develop more sport-specific strength before PHV, training programs should incorporate activities aligned with soccer-specific demands, such as exercises that combine deceleration–acceleration patterns and proper changes in direction, potentially integrated with ball-handling skills.

Strength and Limitations

This study has some strengths. Firstly, all young athletes belonged to the same team, trained with the same weekly volume and frequency. Therefore, homogeneity in training programs was established among all participants, ensuring that the specific contribution of plyometric methods could be evaluated. Secondly, the 12-week duration and progressive increase in plyometric load represent two ecological aspects that enhance the reliability and replicability of the training program and consequently the results. Third, the choice of the age of the study sample. There are few studies that have proposed plyometric training already at 9 years of age, filling a gap in research and, therefore, expanding the knowledge of the effects of PT even in subjects still far from PHV.

The authors are aware of the limitations of this study. First, the small sample size limits the generalizability of findings. To maintain an ecological approach within a single club, the sample was restricted, but the size is consistent with other studies on youth soccer players [12,14]. Secondly, the findings may not apply to female soccer players. Future research should explore PT effects in young female athletes. Finally, the focus on prepubertal players precludes direct comparisons with older cohorts. While the findings may extend to females of similar age, further validation is required.

5. Conclusions

Plyometric training significantly enhances lower limb jump performance in preadolescent soccer players compared to standard training. However, these strength gains do not necessarily translate into additional improvements in agility performance. The present study supports the use of PT as a safe and effective training method for young athletes but highlights the need to integrate it with other training approaches to maximize soccer-specific performance. In particular, combining PT with training programs that targets sport-specific skills, such as deceleration–acceleration patterns and changes in direction, may provide a more comprehensive developmental framework for young soccer players. Future studies should further investigate the effectiveness of PT by examining how improvements in eccentric strength relate to change-of-direction ability in young athletes before PHV.